Pilot tones for optical signal wavelength identification and power measurement

m 1 2 21c 1 n 0k0k A method of optical communication includes providing a plurality of optical signals each associated with a distinct channel of a composite optical signal. A unique pilot tone signature is superimposed on each channel. The spectral composition of each signature includes a plurality of frequencies. In one embodiment, binary frequency shift keying at a frequency fis used to shift between instantaneous frequencies fand fwherein f+Δf=f−Δf=f. Choosing produces a spectrum having a plurality of dominant components at least some of which have substantially the same amplitude. A method of detecting the presence of a selected pilot tone signature having a plurality n of dominant spectral components F. . . Fincludes generating a power spectrum P(f). S(f) is calculated as a product of a plurality of frequency shifted versions of P(f), where k∈{1 . . . n}. The existence of a dominant spectral component at Findicates the presence of the selected pilot tone signature.